1. Field of the Invention
This invention relates to a blood oxygenator or artificial lung of the type comprising a bundle of hollow fibers for oxygenating blood through gas exchange.
2. Prior Art
One conventional artificial lung or oxygenator 50 shown in FIGS. 1 and 2 comprises a tubular housing 52 of a synthetic resin having upper and lower end portions 54a and 54b of an enlarged diameter, and a bundle 56 of hollow fibers 57 disposed within the tubular housing 52. Each of the hollow fibers 57 is made of a microporous, gas permeable material such as a polycarbonate membrane, a porous polypropylene membrane, a porous polyethylene membrane, a regenerated cellulose membrane, a polysulfone, a porous nylon membrane, a porous polyester membrane, a porous acryl membrane or a porous fluorine plastics membrane. Each hollow fiber 57 has an inner diameter of 30 to 1000 .mu.m. The upper end portion 54a has a blood inlet 58 for introducing blood into the housing 52 while the lower end portion 54b has a blood outlet 60 for discharging the blood from the housing 52. A pair of end caps or closure members 62 and 64 are attached to the upper and lower ends of the housing 52, respectively, the end cap 62 having a gas inlet 66 for introducing gas into the housing 52 while the other end cap 64 has a gas outlet 68 for discharging the gas from the housing 52. The opposite ends of the hollow fibers 57 of the bundle 56 are secured to the upper and lower end portions 54a and 54b, respectively, by fastening elements 70a and 70b of a potting resin such as a polyurethane resin and a silicone resin. A pair of seal ring 71a and 71b are carried by the caps 62 and 64, respectively, and are held in sealing engagement with the fastening elements 70a and 70b, respectively. A pair of peripheral retainer flanges 72a and 72b are formed on the inner surface of the housing 52, and a tube 74 of a flexible membrane with a thickness of 0.03 to 1.9 mm such as silicone rubber and latex rubber is disposed within the housing, and the opposite ends of the tube 74 are turned outwardly on the outer surfaces of the flanges 72a and 72b. The turned ends of the tube 74 are sealingly secured to the flanges 72a and 72b by a suitable adhesive. A port 76 is formed on the housing 52 and communicates into the interior of the housing 52 between the upper and lower flanges 72a and 72b, the port 76 being connectable to a fluid source such as a compressor for supplying fluid such as air to the interior of the housing 52 via the port 76. With this construction, upon application of the fluid to the interior of the housing 52 via the port 76, the flexible tube 74 is urged radially inwardly to provide a chamber 78 defined by the outer peripheral surface of the tube 74 and the inner peripheral surface of the housing 52.
In operation, an oxygenating gas, such as oxygen, a mixture of oxygen and air and a mixture of oxygen, air and carbon dioxide, is introduced into the end cap 62 via the gas inlet 66 and caused to pass through the internal bores of the hollow fibers 57 of the bundle 56, the gas being discharged from the end cap 64 via the gas outlet 68. And, blood is introduced into the housing 52 via the blood inlet 58 and is caused to pass along the hollow fibers 57 toward the blood outlet 60. At this time, the oxygen in the oxygenating gas flowing through the hollow fibers diffuses through the porous walls thereof and is brought into contact with the blood to oxygenate it while carbon dioxide in the blood passes through the walls of the hollow fibers thereinto. Thus, the oxygenating of the blood is achieved by such gas exchange as is well known in the art.
When the oxygenating gas and the blood are applied to the oxygenator 50, the hollow fibers 57 of the bundle 56 tend to be displaced toward the axis of the bundle 56. As a result, the outer periphery of the bundle 56 is spaced considerably from the inner peripheral surface of the housing 52, so that most of the blood introduced into the housing 52 passes through a space defined between the outer periphery of the bundle 56 and the inner peripheral surface of the housing 52. Therefore, the blood is not adequately oxygenated. To overcome this difficulty, the fluid under pressure is introduced into the housing 52 via the port 76 to flex the tube 74 radially inwardly toward the outer periphery of the bundle 56 to provide the chamber 78, so that the blood passes through the spaces between the hollow fibers 57 to enhance the oxygenating of the blood. However, this conventional oxygenator or artificial lung 50 is rather expensive to manufacture since the chamber 78 must be provided to achieve a desired oxygenating of the blood.